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Standards and Practices
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Dolby Digital and Dolby E
Bitstreams
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Issue 3
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
Dolby Laboratories, Inc.
Corporate Headquarters
Dolby Laboratories, Inc.
100 Potrero Avenue
San Francisco, CA 94103-4813
Telephone 415-558-0200
Fax 415-863-1373
www.dolby.com
European Headquarters
Dolby Laboratories
Wootton Bassett
Wiltshire SN4 8QJ, England
Telephone (44) 1793-842100
Fax (44) 1793-842101
Dolby, Pro Logic, and the double-D symbol are registered trademarks of Dolby Laboratories.
Surround EX is a trademark of Dolby Laboratories.
All other trademarks remain the property of their respective owners.
 2002 Dolby Laboratories, Inc. All rights reserved.
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Issue 3
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
Table of Contents
1
Scope and Purpose .............................................................................................. 1
2
Definitions ............................................................................................................. 1
2.1
Dolby Digital ............................................................................................... 1
2.2
Dolby E....................................................................................................... 1
2.3
Metadata .................................................................................................... 2
2.4
Integrated Receiver Decoders (IRD) and Set-Top Boxes (STB) ................ 2
2.5
Dolby Digital Surround EX.......................................................................... 2
3
Perceptual Coding vs. Metadata ........................................................................... 3
3.1
The Sound of Perceptual Coding as Implemented in Dolby Digital ....... 3
3.2
The Sound of Metadata.............................................................................. 3
3.3
The Three Ds: Dialogue Normalization, Dynamic Range Control,
and Downmixing......................................................................................... 4
3.4
Dialogue Normalization .............................................................................. 4
3.5
Dynamic Range Control ............................................................................. 6
3.6
Downmixing................................................................................................ 8
4
DVD Authoring System Overview ....................................................................... 10
4.1
DP569/DP562 with Dolby Recorder ......................................................... 10
4.2
DP570/DP569 with Dolby Recorder ......................................................... 11
4.3
Surround EX Encoding with DP570/DP569/EX-EU4 and
Dolby Recorder ........................................................................................ 12
5
DTV Authoring Overview .................................................................................... 13
5.1
Metadata in Master Control ...................................................................... 13
5.2
DP570/DP571 for Digital Television Distribution ...................................... 14
6
Frequently Asked Questions ............................................................................... 16
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
1
Scope and Purpose
Dolby Laboratories has developed products and technologies that enable audio
professionals to create their own Dolby Digital data streams, allowing greater control
and precision. This document is intended to encourage the use of these tools by
mixers, engineers, producers, and directors to master their own audio.
Authoring Dolby Digital bitstreams is a mastering process, and great care should be
taken to properly select the metadata parameters that control the consumer’s decoder
or set-top box and affect the listening experience. It is therefore important to keep this
process as close to the creation of the content as possible so that the intent of the artist
is conveyed accurately to the consumer. The use of Dolby tools and technologies in
the authoring process provides the artist and/or producer unprecedented control over
how their work is experienced by the consumer.
2
Definitions
2.1
Dolby Digital
Dolby Digital (AC-3) is intended for the transmission of audio into the home through
digital television broadcast (either high or standard definition), DVD, or other media.
Dolby Digital can carry anywhere from a single channel of audio up to a full 5.1channel program, including metadata. In both digital television and DVD, it is
commonly used for the transmission of stereo as well as full 5.1 discrete audio
programs. Dolby Digital is designed for maximum fidelity and space efficiency, and
should only pass through one encode/decode cycle.
2.2
Dolby E
Dolby E is specifically intended for the distribution of multichannel audio within
professional production and distribution environments. Any time prior to delivery to
the consumer, Dolby E is the preferred method for distribution of multichannel/multiprogram audio with video. Dolby E can carry up to eight discrete audio channels
configured into any number of individual program configurations (including metadata
for each) within an existing two-channel digital audio infrastructure. Unlike Dolby
Digital, Dolby E can handle many encode/decode generations, and is synchronous
with the video frame rate. Like Dolby Digital, Dolby E carries metadata for each
individual audio program encoded within the data stream. The use of Dolby E allows
the resulting audio data stream to be decoded, modified, and re-encoded with no
audible degradation. As the Dolby E stream is synchronous to the video frame rate, it
can be routed, switched, and edited in a professional broadcast environment.
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
2.3
Metadata
Metadata is additional control information that is carried along with the encoded
audio program and provides essential information about the audio to a Dolby Digital
decoder. Metadata provides many important functions including dynamic range
control for less-than-ideal listening environments, level matching between programs,
downmixing information for the reproduction of multichannel audio through fewer
speaker channels, and other information. Metadata makes Dolby Digital a complete
delivery system for audio, rather than just an audio compression system.
2.4
Integrated Receiver Decoders (IRD) and Set-Top Boxes (STB)
When receiving digital television broadcasts, whether via terrestrial, cable, or satellite
transmission, either an integrated receiver or a set-top box is needed to separate the audio
and video components from the carrier signal. Every STB has a built-in Dolby Digital
decoder that supplies an analog stereo downmix of the program audio (either Lt/Rt or
Lo/Ro, see Section 3.6 for more information). Some STBs may also offer a mono signal
(derived from the Lo/Ro signal) modulated over an RF/antenna output. In addition to
these outputs, a digital output is provided for connection to an external decoder.
2.5
Dolby Digital Surround EX
Dolby Digital Surround EXTM is an extension to the Dolby Digital 5.1 format. It was
introduced to the movie-going public with Star Wars: Episode One—The Phantom
Menace. Originally developed for theatres, this format has migrated into consumer
products and media. Surround EX is primarily used for DVD soundtracks, although it
may be incorporated into the broadcast chain at some point in the future.
The format itself is different from that found in a conventional 5.1 home theater
environment. A back surround channel is added, creating a center surround channel
between the left and right surround speaker channels. This additional “center” or back
surround channel is achieved through a matrix encode of the three discrete surround
channels (Ls, Bs, Rs) during the audio mastering process. This creates a stereocompatible Lst/Rst (Left Surround Total, Right Surround Total) for the surround
channels. In this way, a DVD released in the Surround EX format is compatible with
all existing home theater configurations.
The metadata stream contains a specific parameter that can be flagged to indicate that
the Dolby Digital audio stream is encoded in Surround EX. This metadata parameter
is informational only, and simply allows those consumer decoders that are capable of
decoding in the Surround EX format to switch automatically into this mode.
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
3
Perceptual Coding vs. Metadata
It is generally not necessary to monitor the Dolby Digital coding process from encode
to decode simply to preview the effects of the coding algorithm. However, it is very
important to monitor the effects of metadata on the source audio either through the
encode/decode process or through the use of a DP570 Multichannel Audio Tool. The
simple reason is that the Dolby Digital encoding process is specifically designed to be
transparent, while metadata is intended to optimize the program audio for playback in
a variety of home listening environments.
3.1
The Sound of Perceptual Coding as Implemented in
Dolby Digital
Dolby Digital is a data reduction technology that achieves data compression through
the removal of redundant audio information. The audio reproduced through a Dolby
Digital decoder is not identical to the original source audio. During encoding, the
Dolby Digital algorithm selects the portions of the audio that would not normally be
heard by the human ear and removes them through a process known as Perceptual
Coding. Perceptual coding uses the natural properties of the human ear to ignore
signals masked by adjacent frequencies and the differences in level found within full
bandwidth program audio. More information of the specifics of perceptual coding can
be found in several publications on the Dolby website, www.dolby.com.
The Dolby Digital encoded/decoded signal sounds perceptually the same as the original
audio signals. The masking properties of the human ear allow Dolby Digital to achieve a
better than 15:1 compression ratio from original source digital audio with little or no
perceived difference.
The ratio varies based on applicable sampling rates, Dolby Digital data rates, and bit
resolution. Dolby Digital preserves the resolution of the source digital audio.
Note: Sample rate conversion in the DP569 Dolby Digital Multichannel Encoder,
when enabled, limits the encoded signal to a maximum 20-bit resolution.
However, the DP569 is capable of 24-bit resolution when the sample rate
converter is disabled.
The Dolby Digital coding system is designed to preserve the fidelity of the original
source audio, and nearly ten years of critical use by audio professionals in DVD, film,
multimedia, and broadcast has proven it to be a reliable, accurate, and transparent
coding system.
3.2
The Sound of Metadata
Unlike the nuts and bolts of the perceptual coding process, which is designed to be
audibly identical to the source master, metadata is specifically intended to optimize
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
the sound of the decoded program based upon a consumer’s listening conditions. It is
therefore vitally important to monitor the effects of metadata while mastering a Dolby
Digital data stream.
Metadata provides the tools necessary for audio programs to be reproduced accurately
and artistically in many different listening situations from full-blown home theaters to
in-flight entertainment, regardless of the number of speaker channels, quality of
playback equipment, or relative ambient noise level. While an engineer or content
producer takes great care in providing the highest quality audio possible within their
program, they have no control over the vast array of consumer electronics or listening
environments that will attempt to reproduce the original soundtrack. Metadata
provides the engineer or content producer greater control over how their work is
reproduced and enjoyed in almost every conceivable listening environment.
3.3
The Three Ds: Dialogue Normalization, Dynamic Range
Control, and Downmixing
Metadata provides a number of key parameters that are specifically designed to
control the sound of the program delivered to the consumer, depending upon
selections made at the consumer’s decoder that reflect their unique listening
environment. These metadata parameters are known generally as Dialogue
Normalization, Dynamic Range Control, and Downmixing.
Note: Rather than a single metadata parameter, the function of Downmixing within
the consumer’s Dolby Digital decoder is controlled by several specific
metadata parameters, and, as with the other two Ds, care must be taken in
monitoring and selecting these metadata parameters.
The engineer is ultimately responsible for optimizing the multichannel mix for best
reproduction in the optimal listening environment so care should be taken to ensure
that less optimal listening environments consisting of fewer speaker channels or high
ambient noise levels are supported. For example, enjoyment of a DVD, game console,
or digital television program should not be limited to only those consumers with fullblown home theater systems. Dolby Digital and metadata together provide a method to
achieve the highest quality audio reproduction without compromising the integrity of
the original encoded audio, regardless of the number of speaker channels, relative
ambient noise levels, or quality of equipment in a playback system.
3.4
Dialogue Normalization
The Dialogue Normalization (also known as Dialogue Level or Dialnorm) parameter
within the Dolby Digital stream provides a relative value to the home decoder or settop box that adjusts the audio to a predetermined replay loudness level. This value
aids in level matching between program content and media types (i.e., DVD, DTV,
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
DBS, etc.). Setting the Dialogue Normalization parameter is crucial to the proper
operation of home decoders and provides three main functions:
1. In multimedia postproduction, the level-matching of dialnorm allows different
content (i.e., titles, short movies, game replays, etc.) to be interspersed,
maintaining the same comfortable listening level in the home. During the digital
broadcast of a television program, dialnorm allows commercials, news breaks,
and the like to be interspersed within the program so that the viewer doesn’t have
to constantly reach for the volume control during breaks.
2. Consumer requirements for home enjoyment of multichannel audio vary widely. Not
everyone who owns a DVD player or receives a digital television broadcast listens in
an ideal home theater environment; for example, many laptop computers offer DVD
players and DTV receivers. The specifications, price, and capabilities of speakers,
amplifiers, DVD players, etc., range from the basic to near-professional. Some care
must be taken so that consumers of multichannel audio programs can be reasonably
assured that the mixer’s intent will be carried through their chosen playback system
to their ears. In addition to level-matching between different program content and
media, dialnorm ensures that the full dynamic range of the program can be
reproduced without clipping the digital-to-analog (D/A) converters. As this level shift
occurs well before the consumer’s volume control knob, the decision on how loud to
listen to a particular program is still up to the consumer.
3. A properly set dialnorm value provides the null band within the dynamic range
profile (see Section 3.5) where the audio level is neither raised nor lowered.
Without a properly set dialnorm parameter, reduced dynamic range listening modes
may not have the intended effect of allowing softer portions of the signal to be
audible while simultaneously reducing the decibel level of explosions, gunshots, or
similar effects that may disturb others in the home.
Typically, consumers of a DVD movie or digital television program set their system’s
playback volume to a comfortable level centered around the level of dialogue within
the program. This comfortable listening level depends on the consumer’s taste and the
intelligibility of the dialogue component. The parameter is called “Dialogue
Normalization” because it uses the knowledge of the dialogue level within a program
to make sure the consumer’s comfortable listening level remains consistent between
programs. This concept is derived from a standard practice in film mixing.
That is not to say that dialogue is required to set the Dialogue Normalization
parameter. In music-only DVDs or television broadcasts, the dialnorm parameter can
be thought of as the average volume level of the program.
Dialogue Normalization, in simple terms, is exactly the same as turning the volume
down a bit on a consumer’s home stereo. However, simply adjusting the volume on a
home stereo provides none of the other advantages of dialnorm: providing a reference
for reduced dynamic range listening conditions, accurate and musical dynamic range
compression, and clipping protection prior to the D/A circuitry.
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
Dialogue Normalization in a Dolby Digital decoder cannot be defeated. Dialogue
Normalization alone does not assert any compression or expansion on the program
material but simply adjusts the audio to a standardized level (See ATSC A52
www.atsc.org/Standards/stan_rps.html).
That being said, Dialogue Normalization works in partnership with two other
optionally assertable (or defeatable) parameters within the Dolby Digital bitstream,
collectively called the Dynamic Range Control Profiles. The Dialogue Normalization
parameter determines the area within the program audio where the Dynamic Range
Profiles are inactive, setting a null band between the soft and loud portions of the
program where no audio processing occurs and defining the upper and lower limits of
the Dynamic Range Profiles.
Again, while the Dialogue Normalization parameter is required and not defeatable,
the Dynamic Range Profiles are optional and can be turned off in a properly
implemented Dolby Digital decoder. This means the choice to listen to a program at a
reduced dynamic range (so as not to disturb the neighbors), or to the same program in
all its full-volume, earth-shaking glory, is entirely up to the consumer.
3.5
Dynamic Range Control
Dynamic Range Control (also known as Dynamic Range Compression) within the
Dolby Digital data stream consists of two profiles: Line Mode and RF Mode. These
two profiles do not change the content of the encoded audio within the bitstream, but
are used by the Dolby Digital decoder to adjust the extremes of the program material
within the listening environment to account for those instances where it is preferable
or necessary to listen to the program at a reduced dynamic range.
Line mode provides a moderate amount of compression when compared with RF
mode, and also allows the user to adjust the low-level boost and high-level cut
parameters within a home decoder when not downmixing. This adjustment or scaling
of the boost and cut areas allows the consumer to customize the audio reproduction
for their specific listening environment. To avoid clipping, the scaling feature is not
available in certain downmixing situations. RF mode is designed for peak-limiting
situations where the decoded program is intended for delivery through an RF input on
a television, such as through the antenna output of a set-top box. The RF Mode
Profile is also used for a common feature on consumer decoders known as “Midnight
Mode,” which provides enough dynamic range compression to ensure that an action
movie or game won’t wake up others in the home.
In contrast to compression as used on musical instruments in a recording studio to
make them sound punchy and fat, dynamic range compression limits the softest and
the loudest portions of an audio program to maintain a comfortable and intelligible
listening level. For example, when enjoying a movie (on DVD, video, or broadcast
TV) at lower volumes, the softer portions of the program (whispers, softer dialogue,
etc.) are more difficult to hear, requiring greater volume, thereby making the louder
portions (explosions, onscreen arguments, gunshots, etc.) too loud for comfortable
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
Dialogue Level
Setting
Null
Band
Low
Early
Cut
Range
Cut
Range
Centered at
the Dialogue
Level Parameter
Boost
Range
Low
Ouput Level
High
listening. Additionally, when enjoying a television broadcast or DVD in an
environment with a high level of ambient noise, quieter portions of the program are
drowned out by the ambient noise. When these “Dynamic Range Profiles” are
asserted within the decoder, the decoder raises the level of the softer portions of the
program and lowers the level of the louder portions, allowing the user to enjoy the
movie without having to reach for the volume control constantly.
Input Level
High
Figure 1 Dynamic Range Control within a Dolby Digital Decoder
There are two dynamic range metadata profiles to set within a Dolby Digital data stream.
Each of these two profiles has six presets available to choose from, including None.
Music Light (No early cut range)
Max Boost: 12 dB (below –65 dB)
Boost Range: –65 dB to –41 dB (2:1 ratio)
Null Band Width: 20 dB (–41 dB to –21 dB)
Cut Range: –21 dB to +9 dB (2:1 ratio)
Film Standard
Max Boost: 6 dB (below –43 dB)
Boost Range: –43 dB to –31 dB (2:1 ratio)
Null Band Width: 5 dB (–31 dB to –26 dB)
Early Cut Range: –26 dB to –16 dB (2:1 ratio)
Cut Range: –16 dB to +4 dB (20:1 ratio)
Music Standard
Max Boost: 12 dB (below –55 dB)
Boost Range: –55 dB to –31 dB (2:1 ratio)
Null Band Width: 5 dB (–31 dB to –26 dB)
Early Cut Range: –26 dB to –16 dB (2:1 ratio)
Cut Range: –16 dB to +4 dB (20:1 ratio)
Speech
Max Boost: 15 dB (below –50 dB)
Boost Range: –50 dB to –31 dB (5:1 ratio)
Null Band Width: 5 dB (–31 dB to –26 dB)
Early Cut Range: –26 dB to –16 dB (2:1 ratio)
Cut Range: –16 dB to +4 dB (20:1 ratio)
Film Light
Max Boost: 6 dB (below –53 dB)
Boost Range: –53 dB to –41 dB (2:1 ratio)
Null Band Width: 20 dB (–41 dB to –21 dB)
Early Cut Range: –26 dB to –11 dB (2:1 ratio)
Cut Range: –11 dB to +4 dB (20:1 ratio)
The details of the dynamic range characteristics for each preset are shown for
reference only and are not adjustable, and, as mentioned previously, the dialogue
normalization value determines the placement of the null band. Upon decoding,
however, a customer has the option of scaling the amount of boost or cut, depending
on the feature set available in their home decoder. Once again, the ability to scale
only applies to Line mode.
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
Because of the relationship between dialogue normalization and dynamic range
control, it is necessary to select the appropriate dialnorm value prior to previewing
dynamic range profiles. As the amount of dynamic range compression used is
ultimately selected by the consumer for their own specific listening needs, it is
important to preview the dynamic range control profiles through a variety of
compression settings before selecting one to include in the metadata stream.
3.6
Downmixing
Simply put, downmixing allows consumers to enjoy a 5.1-channel television
broadcast, DVD, or game console without requiring a complete home theater setup.
More technically, downmixing is a function of Dolby Digital that allows a
multichannel program to be fully reproduced over fewer speaker channels than for
which the program is optimally intended.
As with stereo mixing, where the mix is monitored in mono on occasion to maintain
compatibility, multichannel audio mixing requires the engineer to reference the mix
to fewer speaker channels to ensure compatibility for downmixing situations. In this
way, Dolby Digital, using the metadata parameters that control downmixing, is an
“Equal Opportunity Technology” in that every consumer who receives the Dolby
Digital data stream can enjoy the best audio reproduction possible, irrespective of the
number of channels in their playback system.
It is important to understand the output signals found on each piece of equipment that
can receive a Dolby Digital program in the home (see Table 1). Set-top boxes (STB),
such as those used for the reception of terrestrial, cable, or satellite digital television
typically offer an analog mono signal modulated on the RF/Antenna output, a line
level analog stereo signal, and an optical or coaxial digital output. DVD players offer
an analog stereo signal as well as a digital output, and possibly six-channel analog
outputs as well. Portable DVD players offer an analog stereo signal, headphone, and
digital outputs. DVD players found in computers and game consoles offer a digital
output and possibly six-channel analog outputs, as well as analog stereo and
headphone outputs. 5.1-channel amplifiers, decoders, and receivers have six-channel
analog outputs and possibly six speaker-level outputs.
In all cases, the analog stereo output is a downmixed version of the Dolby Digital
data stream while the digital output carries the Dolby Digital data stream to a
downstream decoder or integrated amplifier with Dolby Digital capability.
The analog stereo output of these units can be one of two different stereo downmixes.
One is a stereo-compatible Dolby Surround downmix of the multichannel source
program that is suitable for Dolby Surround Pro Logic decoding. This downmix is
called left-total/right-total or Lt/Rt. The other type of downmix is a simple stereo
representation (called left-only/right-only, or Lo/Ro) suitable for playback on a stereo
hi-fi or via headphones, and from which a mono signal is derived for use on the
RF/Antenna output from a set-top box. The difference between the two downmixes is
how the surround channels are handled. The Lt/Rt downmix sums the surround
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
channels and adds them in phase to the left channel and out of phase to the right
channel. This allows a Dolby Surround Pro Logic decoder to reconstruct the L/C/R/S
channels for a Pro Logic home theater. The Lo/Ro downmix adds the left and right
surround channels discretely to the left and right speaker channels. This preserves the
stereo separation for stereo-only monitoring and provides a mono-compatible signal.
The LFE channel is not included in either of these downmixes.
On most equipment, the consumer can, through the product’s user interface, choose
the appropriate downmix for their playback system. Certain metadata parameters
allow the engineer to select how the stereo downmix is constructed and which
downmix is preferred, although the Lt/Rt downmix is usually the default.
As previously mentioned, user adjustment of Dynamic Range Control (DRC) is
limited while downmixing; the use of the stereo analog outputs of DVD players, settop boxes, and game consoles are no different. Typically, the consumer is not able to
adjust the cut or boost parameters when using the stereo outputs and the only DRC
available is the selection of a “Midnight Mode” or the equivalent.
Some metadata parameters assist in achieving an appropriate downmix, helping to ensure
that the intention of the engineer/content producer translates correctly across these
environments. Specifically, metadata provides control over how certain channels are
“folded” into the resulting downmix. As with DRC, downmixing is ultimately the choice
of the consumer and dependent upon their unique listening environment.
While the engineer is tasked with optimizing the multichannel mix for reproduction in
an ideal monitoring environment, it is important to reference the mix in downmixing
conditions to ensure cross-platform compatibility and the proper selection of the
downmixing metadata parameters. The many different consumer listening modes can
be heard through front-panel selections on either the DP562 Reference Decoder or the
DP570 Multichannel Audio Tool.
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
Table 1 Example of Consumer Products and Output Options
5.1-Channel
Amplifier
5.1-Channel
Decoder
High-End
DVD Player
DVD Player
Digital
I/O
5.1-Channel
Analog Outputs
X
X
Two-Channel
Analog Outputs
RF
Remodulated
Output
Notes
The regular A/V amp
X
X
X
X
X
(X)
X
X
X
X
X
X
Often HDTV
X
X
X
IDTV
X
X
High-End
TV
X
Usually SDTV
TV set with an integrated
digital TV tuner
Large screen TV with 5.1
speakers
PC
High-End
Set-Top Box
Set-Top Box
X
Includes games consoles
X
4
DVD Authoring System Overview
4.1
DP569/DP562 with Dolby Recorder
This the most common setup for Dolby Digital encoding and decoding in use today. It
provides a Dolby Digital bitstream that can be stored on a PC computer and used
within any DVD authoring package as well as for reference decoding. It has also been
used in mixing situations, since configuring an encoder back-to-back with a decoder
was the only way to monitor the effects of metadata on program audio, until the
introduction of the DP570 Multichannel Audio Tool.
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
DP569 Dolby Digital
Encoder
Mixed audio stems
to DP569
Dolby Digital
output
PC running
Dolby Recorder application
Timecode
Dolby Digital
DP562 Dolby Digital
Decoder
Audio out to
amps/monitoring system
Figure 2 DP569/DP562 with Dolby Recorder
This method, while effective, suffers from two main drawbacks.
1. The resulting audio from the decoder is out of sync with the picture. The coding
delay inherent in the encoder, coupled with the latency of the decoder, creates a
minimum overall sync error of about 219 ms. The coding delay within Dolby
Digital encoders is adjustable from a minimum of 187 ms up to a maximum of
450 ms, while Dolby Digital decoders, adhering to SMPTE 337M, add a latency
of 32 ms on the decode side. While the resulting audio gives the engineer an
accurate representation of the effects of the selected metadata parameters, the
delays involved create a less-than-ideal monitoring situation.
2. This configuration provides no method to use common console functions such as
Solo/PFL and Speaker Dim/Mute during mastering. As the monitoring system is
connected to the output of the DP562 in this configuration, any solo or dim/mute
functions existing on the console cannot be used.
These three issues notwithstanding, using an encoder and decoder back-to-back
provides an accurate method of selecting and previewing metadata parameters for the
creation of a Dolby Digital data stream, as well as creating the actual stream itself.
4.2
DP570/DP569 with Dolby Recorder
The preferred method of selecting, previewing, and authoring metadata for inclusion
within a Dolby Digital data stream is through the use of the DP570 Multichannel
Audio Tool paired with the DP569 Encoder. This configuration uses the DP570 for
both the monitoring and authoring functions of metadata, and frees the DP569 to
simply encode the audio and create the resulting Dolby Digital data stream with the
selected metadata parameters.
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
Emulator out to
amps/monitors
DP570 Multichannel
Audio Tool
Mixed audio stems
to DP570
Console
solo bus
Audio router output
Timecode
Metadata
DP569 Dolby Digital
Encoder
Dolby Digital
output
PC running
Dolby Recorder application
DP562 Dolby Digital
Decoder
For file confidence monitoring
Figure 3 DP570/DP569 with Dolby Recorder
This configuration provides several key features.
1. The DP570 Multichannel Audio Tool provides the ability to monitor the effects of
metadata in real time, without the delays found in an encode/decode configuration.
This allows audio and picture to remain synchronous while selecting and previewing
various metadata parameter settings.
2. The software remote and graphical user interface (GUI) provide a simple procedure
for the measurement and selection of the Dialogue Normalization (dialnorm)
parameter. As dialnorm is the single most important parameter in the metadata
stream, this procedure helps eliminate the guesswork in setting this important value.
3. The metadata selections made are automatically forwarded to the DP569 encoder,
limiting user input to a single, user-friendly device in the selection and preview of
metadata.
4. The solo bus within the console is still active, and the DP570 provides dim and mute
functions for audio production. Additionally, the DP570 provides a General Purpose
Input/Output (GPI/O) connector for external control of key features within a consoledriven hardware remote control. This allows many controls within the DP570 to be
located close to the engineer and even integrated within the console itself.
4.3
Surround EX Encoding with DP570/DP569/EX-EU4 and Dolby
Recorder
This configuration, a modification of the previous one, prepares, creates, and
monitors a Dolby Digital bitstream encoded in Surround EXTM for DVD.
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Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
EX-EU4 Dolby EX Surround Encoder
0101
Ls/Bs/Rs
stems to
SEU-4EX
Lt/Rt output
to Ls/Rs input
through A/D
DP570 Multichannel Audio Tool
Emulator out to
amps/monitors
L/R, C/LFE
stems to
DP-570
Timecode
Dolby Digital
output
Metadata
Digital audio router
output: L/R,C/LFE, Ls/Rs
Console
solo bus
DP569 Dolby Digital Encoder
PC running
Dolby Recorder application
DP562 Dolby Digital Decoder
For file confidence monitoring
Ls/Rs analog
output for
EX decoding
EX-DU4 Dolby EX Surround Decoder
Figure 4 Surround EX Encoding with DP570/DP569/EX-EU4 and Dolby Recorder
As in the previous example, the console master functions are still active and the
DP570 provides dim and mute functions for audio production.
The mixed “6.1” stems from the console are separated, and the surround channels (Ls,
Bs, Rs) are sent to the EX-EU4 while the front channels (L, R, C, LFE) are sent
directly to the DP570 (appropriate A/D or D/A conversion is implied). After encoding
the three surround channels in real time as analog audio, the Lt/Rt output of the EXEU4 is sent to the Ls/Rs inputs on the DP570 after A/D conversion. When the EX
button is pressed on the DP570, the DP570 performs a Pro Logic decode on the Ls/Rs
inputs and sends the decoded signals to the appropriate speaker channels for
production monitoring.
Standard coding delays are present within the DP569 Dolby Digital Encoder, and
standard latencies are present during confidence checking through the DP562 decoder.
In this example, the analog outputs of the DP562 are used to relay the Ls/Rs channels
to the EX-DU4 Surround EX Decoder.
5
DTV Authoring Overview
5.1
Metadata in Master Control
Monitoring the effects of metadata on program content in a master control situation
can be simply achieved through the use of the DP570.
13
Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
To router In
Video
Sources
B
Venus2001
DVP
Stream Select
Video
PHILIPS
A Flag
A
B Flag
MetaData Sw
B
Metadata
Metadata
Dolby Digital
encoded audio
CH 1&2 or stereo
B
Dolby E
or
stereo audio
Dual DP572
Dolby E Decoders
CH 3&4
6-channel (5.1)
or
stereo audio
CH 5&6
DP569 Dolby Digital
Encoder
DAP
DAP
6-channel (5.1)
or
stereo audio
DAP
Monitoring system
DP570 Multichannel Audio
Tool
Metadata
Figure 2 Multichannel Monitoring in Master Control for Digital Television
This block diagram shows a simplified master control switch between two sources.
Prior to entering master control, the incoming Dolby E streams are decoded back to
baseband PCM audio. The metadata for each incoming Dolby E stream is sent
through a serial metadata switcher whose output feeds a downstream DP569 Dolby
Digital Encoder for transmission, as well as a DP570 Multichannel Audio Tool in the
monitor chain. The DP570 controls the monitoring environment and receives the
appropriate audio feeds from either of the two sources in this example.
5.2
DP570/DP571 for Digital Television Distribution
The preferred method of selecting, previewing, and authoring metadata for inclusion
within a Dolby E data stream is through the use of the DP570 Multichannel Audio
Tool paired with the DP571 Dolby E Encoder. This configuration uses the DP570 for
both the monitoring and authoring functions of metadata, and frees the DP571 to
simply encode the audio and create the resulting Dolby E data stream with the
selected metadata parameters.
14
Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
Emulator out to
amps/monitors
DP570 Multichannel Audio
Tool
Mixed audio stems
to DP570
Video Sync
Dolby E Output
Console
solo bus
Audio router output
Metadata
(one frame delay)
00:00:00:00
DP571 Dolby E Encoder
Digital VTR
Figure 3 DP570/DP571 for Digital Television Distribution
The output of the DP571 is delayed one video frame from reference. Upon decode of
the Dolby E stream, the DP572 Dolby E Decoder adds another frame of delay from
the reference.
This configuration provides several key features.
1. The DP570 Multichannel Audio Tool provides the ability to monitor the effects of
metadata in real time, without the latencies (and expense) inherent in using a
Dolby Digital encoder and decoder in a back-to-back configuration. This allows
audio and picture to remain synchronous while selecting and previewing various
metadata parameter settings.
2. The software remote and GUI provide a simple and automatic procedure for the
measurement and selection of the dialnorm parameter. As dialnorm is the single
most important parameter in the metadata stream, this procedure eliminates the
guesswork in setting this important value.
3. The metadata selections made are automatically forwarded to the DP571 encoder,
limiting user input to a single, user-friendly device.
The solo bus within the console is still active and the DP570 provides dim and mute
functions for audio production. Additionally, the DP570 provides a GPI/O connector
for external control of key features within a console-driven hardware remote control.
This allows many controls within the DP570 to be located close to the engineer and
even integrated within the console itself.
15
Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
6
Frequently Asked Questions
Aren’t Dolby Digital and “5.1” the same thing?
No. A stream encoded in Dolby Digital can carry any number of channels, from a
minimum of one mono signal to a maximum of six channels in a 5.1-channel home
theater configuration. In digital television broadcast, Dolby Digital is commonly used
in a two-channel stereo configuration. The flexibility of Dolby Digital as an encoding
technology to carry anywhere from mono to multichannel surround programs makes
it the ideal tool to carry audio in digital media.
Aren’t Surround EX and “6.1” (or even “7.1”) the same thing?
No. Dolby Digital Surround EXTM was first introduced to the public with the release of
Star Wars: Episode One—The Phantom Menace. Since then, many more films have
been released in theatres in the Surround EX format. Now, Surround EX is appearing
on DVDs and consumer electronic equipment for use in the home.
The Surround EX format is different from conventional 5.1 in that an extra back
surround channel is added between the left and right surround channels. To maintain
compatibility, this back surround channel is matrix-encoded with the left/right
surround channels to create a stereo-compatible surround signal. Consumers without
Surround EX capability receive stereo surround channels, while those with Surround
EX decoding capability hear three surround channels. The Surround EX format is
only valid on source signals with at least two surround channels.
How do I set up the speakers on my mix stage or production studio for
Dolby Digital or Dolby E authoring?
Since both Dolby Digital and Dolby E are discrete encoding processes (i.e., speaker
channel separation is maintained throughout the process and no channels are
“matrixed”), what is heard on the mix stage is what the consumer will hear at home,
provided the listening environment is properly calibrated. While there is no specific
standard for sound pressure level (SPL) during mastering for DVD or digital
television broadcast, it is important that each speaker is adjusted to deliver the same
SPL at the mixing position. This can be achieved by measuring the SPL with a meter
at the mixing position and making appropriate adjustments while playing pink noise
through each speaker individually. Some mixing stages are set to 85 dB SPL at each
speaker, while others may be set somewhat lower. The important thing is to make
sure that each speaker is set to the same level at the mixing position.
The subwoofer speaker should be calibrated with 10 dB of in-band gain over the
center channel from 25 to 120 Hz when measured with a real-time frequency
analyzer. This would equate to about 91 dBC when measured with a properly
calibrated SPL meter.
16
Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
Additionally, it is important that each of the main channels be equidistant from the
mixing position. If this is not possible, the DP570 Multichannel Audio Tool has builtin delays that can be added to each channel as needed. Please refer to the User’s
Manual for more comprehensive information.
I am recording and mixing a music-only program and I don’t want the
consumer to assert any compression on the audio. What should I do?
While it is often preferred to monitor and select the dynamic range control parameters
for the DVD release or broadcast of a feature film, despite the user-selectable nature
of these parameters they still may not be desired for music-only programs. In these
instances, selecting “None” as the Dynamic Range profile can effectively negate the
dynamic range control parameters. While RF modes will still be active for certain
specific purposes (downmix clipping protection) and the proper setting of the
dialnorm parameter is still critical, setting the profile to “None” prevents the
consumer from asserting any user-selectable dynamic range control.
I’m mixing a film for digital television broadcast. Should I include a
Dolby Digital stream of my final mix along with the discrete tracks?
It depends. Dolby Digital is designed as a one-time decodable technology. If the
program content is to be simply streamed out through a broadcast encoder, including
a Dolby Digital stream on the audio tracks of your digital videotape is acceptable.
This ensures that the metadata parameters you select will be transported to the
consumer’s home decoder, and your content will be heard as you intended.
However, if the program content will be decoded and further processed, edited, or
sweetened, this would be a distribution process and therefore require a different
encoding technology. The accepted coding technology for the distribution of
multichannel audio for digital television broadcast is Dolby E. If Dolby E equipment is
not available, the best choice for the distribution of multichannel audio for DTV is the
original source audio recorded in baseband PCM format on digital multitrack media.
Can I use a 384/448 kbps data rate for stereo?
Yes. All Dolby Digital decoders support up to at least 448 kbps (DVD and DVB max
spec) data rate irrespective of the number of channels encoded within the Dolby
Digital data stream. The final data rate used is a production choice depending on
many factors, including number of audio tracks, video data rates, and available space
for the audio on a DVD or within the transmission stream, among others. While
192 kbps is a common rate for the production of 2/0 (stereo) Dolby Digital data
streams, there is nothing preventing the use of higher data rates, if desired.
17
Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
How can I set the DP562 decoder to emulate the most common dynamic
range control settings on consumer decoders?
The front panel of the DP562 has four buttons that deal with the dynamic range
control settings: None, Custom, Line, and RF. None is a professional set-up mode
that defeats both dynamic range control and dialnorm, and is only used for installation
and signal tests. Once a specific dynamic range profile has been selected, simply
pressing RF emulates the selection of “late night mode” in a consumer decoder, while
Line mode emulates a more moderate dynamic range control effect that a consumer
may select. Line mode within the DP562 decoder also allows limited scalability when
not downmixing.
Custom is commonly used to turn dynamic range control off while still asserting the
dialnorm parameter, which emulates the consumer choosing to listen in a full
dynamic range mode. Some high-end consumer decoders offer a scalable boost and
cut, and Custom mode can be tailored to reflect this as well.
Note: These modes are also included in the DP570 Multichannel Audio Tool.
I’m using a consumer decoder to monitor my Dolby Digital stream. How
do I set it up so that I can use it for mastering my Dolby Digital stream?
While it is preferable to use a reference decoder such as the DP562 for mastering
purposes, it is possible, albeit unwieldy, to use a consumer decoder.
Consumer decoders do not offer easy access to the many downmix and dynamic
range options that may be available to the consumer at home. In addition, not all
consumer decoders offer every feature that is available in Dolby Digital technology.
A reference decoder like the DP562 has all the necessary controls for mastering on
the front panel to facilitate changing downmixing conditions and dynamic range
profiles quickly.
If budget constraints require the use of a consumer decoder, it is suggested that the
engineer refer to the operation manual of the device for specific information.
Why is it called a Low-Frequency Effects (LFE) channel? Isn’t it just the
subwoofer?
Actually, LFE and subwoofer are two very different things.
Typically, the term “subwoofer” refers to a speaker that reproduces very low-frequency
information that the main channel speakers (however many there are) are incapable of
reproducing. Low-frequency sounds that are normally found on the main audio
channels are directed to the subwoofer speaker for added punch in the low range. In this
fashion, a subwoofer acts as a complement to extend the range of the main speakers,
which may find it difficult, if not impossible, to reproduce these low frequencies.
18
Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
The LFE channel in contrast, is specifically produced with low-frequency information
exclusive to this channel. Content producers have specifically created this LFE
channel to include extra sound-effects information for emphasis in effects, such as
explosions, crashes, gunshots, and such.
In a consumer playback environment, often low-frequency information from the main
channels is redirected to the subwoofer speaker and added to the existing LFE
channel, if any. If there is no LFE channel present in the Dolby Digital stream, the
subwoofer speaker contains the low frequencies redirected from the main speakers.
The capability to redirect low-frequency information is called Bass Management, and
is present in all Dolby Digital decoders. The LFE channel can also be redirected to
the main speaker channels through the use of Bass Management, for those playback
environments lacking a subwoofer speaker.
When producing a music-only multichannel program, the entire musical contents of
the program should be placed in the main channels, just as they are in stereo music
recordings. The LFE channel should only be used when the bass levels are so high as
to require a substantial decrease in overall program volume to accommodate them,
such as might occur with the cannon shots in Tchaikovsky’s “1812 Overture.”
Just as with any full-bandwidth audio signal delivered to consumers via DVD, CD, or
DTV, it is the job of the playback system to get the most out of the signal. Consumer
Dolby Digital systems that use a combination of smaller speakers and subwoofers
incorporate bass management to ensure that the speakers most able to reproduce the
bass are used to the best advantage. There is no need to tailor the frequency content of
the program in anticipation of the many different playback systems it may encounter
in the home.
Remember: just because the “point-one” channel is there does not mean it must be
used. It is perfectly acceptable to create a five-channel Dolby Digital stream
(encoding in 3/2 mode, as opposed to 3/2L mode) without an LFE channel present.
Why do I need the Dolby Recorder?
The Dolby Recorder program is a Microsoft Windows-based application that allows a
Dolby Digital data stream to be recorded onto a computer hard drive. It creates a file
with the .ac3 file extension that can then be ported over to a DVD authoring system
and married to the encoded video content.
The DP569 Encoder outputs a Dolby Digital data stream carried within the envelope of
an AES/EBU digital audio pair, although the actual area taken up by the Dolby Digital
data is only a fraction of the AES/EBU space. The rest of the unused area is filled out
with zeros. The AES/EBU envelope allows the Dolby Digital data to be routed and
stored using much of the same equipment that passes AES/EBU digital audio.
However, for a DVD authoring system to use this data stream, the excess zeros must be
stripped off. In simplest terms, this is what the Dolby Recorder application does.
19
Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
How much space does an *.ac3 file consume on my hard drive?
It is simple to calculate the needed disk space for a *.ac3 file. First, determine the
number of seconds in the program. In this example, a 90-minute program and a Dolby
Digital data rate of 448 kbps is used:
5,400 sec. × 448,000 bits per sec. [Dolby Digital data rate] = 2.4192 gigabits
2.4192 gigabits / 8 [for byte conversion] = 302.4 megabytes
I’m not using Dolby Recorder. Can I save my Dolby Digital data stream
to a Digital Audio Tape (DAT)?
While both Dolby Digital and Dolby E data streams can be recorded and routed much
like regular PCM digital audio, the encoded signal is data and specific precautions must
be taken to ensure that it survives any archival process. Any reclocking or resampling
of the data stream destroys it and renders it irrecoverable. However, both Dolby Digital
and Dolby E data fit nicely on the digital audio tracks of many digital video recorders.
Additionally, Dolby Digital can be recorded onto the audio tracks of many digital
multitracks. Most DAT machines do not have the capability of recording data rather than
audio, although some professional units offer this feature. Generally, a DAT is not a good
medium for the archiving of Dolby Digital data streams. Whenever data is recorded onto
a DAT, the possibility of undecoded data being played out of the unit at maximum
volume (0 dB full scale), and possibly damaging speakers and ears, exists if the DAT
machine mistakenly interprets the data as audio or in any way corrupts the data stream.
Can I record Dolby E onto a DAT?
For Dolby E to maintain coherence with video frame boundaries, and thus be able to
be routed and switched much like video signals, it is usually necessary for the
archival medium to be referenced to video.
However, with the introduction of the DP583 Dolby Frame Synchronizer, content
producers now have the ability to archive Dolby E data streams to non-video based
media. The DP583 provides the ability to re-clock the Dolby E stream to a house
video reference, as well as reclocking Dolby Digital and baseband PCM audio to a
house sample clock reference. As with other “audio only” mediums, care must be
taken so that the DAT used to archive the Dolby E data stream is not mistakenly
played back in an audio system.
With the delays involved in using Dolby E, how should I compensate to
maintain lip-sync on playback of a DTV program?
Dolby E delays the audio a single video frame based on the video reference for each
encode or decode cycle. These delays are necessary to process the audio into the data
stream and vice versa. There are two methods to compensate for these delays:
20
Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
1. Record the Dolby E stream so audio and picture are in sync on tape. This requires
advancing the source tracks one frame before encoding to compensate for the one
frame of delay in the Dolby E encoding process. This method maintains audio/picture
sync on the recording media to facilitate editing. Upon decode of the Dolby E data,
the video will have to be delayed one frame to compensate for the one frame of delay
in the decoding process.
2. Record the Dolby E data so the decoded Dolby E data stream will be in sync with
video upon decoding of the data stream.
When using Dolby E with standard definition video, this requires advancing the audio
two frames prior to encoding. This compensates for the single-frame delay during the
encode cycle and the additional single-frame delay on decode. This method is useful to
ensure that there will be no additional video delays or other processing necessary upon
decoding of the data stream, since the audio will be in sync once decoded. This method is
not recommended if the source program will be edited prior to decoding of the Dolby E
data stream.
In the case of Dolby E with high-definition video, HD video machines have built-in
means of compensating for the one-frame Dolby E encoding delay. Upon playback of
the HD tape, the video processing built into the unit compensates for the one-frame
Dolby E decoding delay, thereby maintaining sync with the picture during editing and
upon decoding of the Dolby E data stream.
How do I compensate for encoding delays and decoding latencies when
authoring a Dolby Digital data stream for DVD?
A Dolby Digital data stream can carry time stamp information within each Dolby Digital
synchronization frame. These time stamps originate from the master timecode referenced
to the video content. When a DVD is authored, the authoring system looks at the time
stamps encoded within the Dolby Digital data stream and matches the timecode numbers
between the audio and video components.
When mastering a Dolby Digital data stream for DVD, be sure to include the appropriate
timecode signal to maintain sync with picture within the authoring system.
Does Dolby E replace Dolby Digital?
No. Dolby E is an encoding technology used only for professional distribution of
audio, such as from television networks to affiliates through satellite communication
or via hard media like digital videocassettes. Dolby E is specifically designed to allow
numerous generations of encode/decode cycles that are sometimes necessary for the
production and distribution of audio in a broadcast environment. Dolby Digital is
designed to deliver digital audio to the home through digital television broadcast,
DVD, or other media. As it is optimized for high quality at low data rates, Dolby
Digital encoding should be performed after all final production decisions have been
made and the next decode step would be in the consumer’s home.
21
Standards and Practices for Authoring Dolby® Digital and Dolby E Bitstreams
Can I buy a consumer version Dolby E decoder for my home theater?
No. Dolby E is a professional technology and is not licensed for consumer use.
How do I get from Dolby E to Dolby Digital?
To create a Dolby Digital data stream from a Dolby E stream, it is necessary to
decode the source Dolby E stream to baseband PCM digital audio and then encode
the selected digital audio program using a Dolby Digital encoder.
Where can I learn more about Dolby technologies?
See www.dolby.com for more details about our technologies and products. You can
also find technical information about AC-3 on the Advanced Television System
Committee’s website, www.atsc.org.
22